Abstract
IL-21 is a type I cytokine that is produced by activated CD4+ T cells and has a significant impact on the growth, survival, and functional activation of B lymphocytes. While IL-21 has been identified in several teleost fish species, its function and associated mechanisms focus on teleost fish B cells remain largely unknown. In this study, we aimed to investigate the effects of IL-21 (OnIL-21) on IgM+ B cells from Nile tilapia (Oreochromis niloticus), as well as the intracellular signaling transduction pathway involved. Through intraperitoneal injection of recombinant OnIL-21 (rOnIL-21), we observed that IL-21 exerted significant effects on Nile tilapia IgM+ B cells, including the promotion of IgM+ B cell proliferation, induction of IgM secretion, and up-regulation of inflammatory cytokines. These findings suggest that OnIL-21 enhances the ability of IgM+ B cells in humoral immunity. Furthermore, when IgM+ B cells were stimulated with rOnIL-21 in vitro, we observed a significant up-regulation in antibody secretion ability (sIgM), as well as increased expression of IFN-γ and IL-10. To further understand the regulatory mechanism of OnIL-21, we demonstrated that OnIL-21 binds to its heterodimer receptor complex (OnIL-21R/Onγc) to exert its function. This binding triggers the conserved JAK/STAT3 and AKT pathways, which in turn regulate the expression of genes involved in B cell proliferation, antibody secretion, and cytokine expression. Collectively, our findings establish that IL-21 plays a crucial role in the regulation of humoral immunity in lower vertebrates, and this regulation is mediated through conserved signaling pathways across vertebrates.
Published Version
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